The present invention relates to a gas-impermeable laminate that delaminates into gas-permeable and gas-impermeable portions. More specifically, the invention pertains to packaging for products, such as food (e.g., fresh red meat or poultry) products, that are initially enclosed by the gas-impermeable laminate under certain environmental conditions (e.g., a low-oxygen environment). The initial environmental conditions within the package may subsequently be altered by peelably removing the gas-impermeable portion of the laminate from the gas-permeable portion, thereby allowing air to enter the package to effect a desired change in the packaged product.
Historically, large sub-primal cuts of meat have been butchered and packaged in each supermarket. This arrangement has long been recognized to be inefficient and expensive. It would instead be preferable to butcher and package the meat at a central processing facility which benefits from economies of scale, and then ship the packaged meat to individual supermarkets or other retail outlets such as is done, for example, with many poultry products. It is believed that central processing of meat would also lead to a higher quality, more sanitary product with a longer shelf-life than meat which is butchered and packaged in individual supermarkets.
Fresh red meat presents a particular challenge to the concept of centralized processing and packaging due to its oxygen-sensitivity. Such oxygen-sensitivity is manifested in the shelf-life and appearance (color) of a packaged meat product. For example, while a low-oxygen packaging environment generally increases the shelf-life of a packaged meat product (relative to meat products packaged in an environment having a higher oxygen content), red meat has a tendency to assume a purple color when packaged in the absence of oxygen or in an environment having a very low oxygen concentration, i.e., below about 5% oxygen. Unfortunately, such a purple color is undesirable to most consumers, and marketing efforts to teach the consumer about the acceptability of the purple color have been largely ineffective. When meat is exposed to a sufficiently high concentration of oxygen, e.g., as found in air, it assumes a bright red color which most consumers associate with freshness. After 1 to 3 days of such exposure, however, meat assumes a brown color which, like the purple color, is undesirable to most consumers (and indicates that the meat is beginning to spoil).
Thus, in order to effectively butcher and package meat products in a central facility for distribution to retail outlets, the meat would desirably be packaged, shipped, and stored in a low-oxygen environment for extended shelf-life, and then displayed for consumer sale in a relatively high-oxygen environment such that the meat is caused to xe2x80x9cbloomxe2x80x9d (or, more accurately, xe2x80x9cre-bloomxe2x80x9d) into a red color just before being placed in a retail display case. While in the retail display case, the meat product is desirably contained in a package which protects it from microbial and other contamination. In order to attain the maximum economic benefit from centralized packaging, the package in which the meat product is displayed for consumer sale is the same package in which the meat product is initially packaged and shipped from the central processing facility. As can be appreciated, centralized butchering and packaging of fresh red meat presents a number of difficult packaging challenges.
A variety of packages, known as xe2x80x9ccase-ready packages,xe2x80x9d have been developed in an effort to overcome the foregoing challenges. One type of case-ready package is a peelable xe2x80x9cvacuum-skinxe2x80x9d package (xe2x80x9cpeelable VSPxe2x80x9d). A traditional peelable VSP includes a lidding film that separates into gas-permeable and gas-impermeable portions and which encloses, e.g., a fresh red meat or poultry product that is disposed on a support member. The lid is thermoformable, i.e., capable of being formed into a desired shape upon the application of heat, and is thermoformed about the product on the support member by means of heat and differential pressure. In so doing, the lid is also bonded to the support member outside the periphery of the product. Virtually all of the air is evacuated from the interior of the package so that the lid conforms very closely to the contour of the packaged product. (For further details see, e.g., U.S. Pat. Nos. Re 30,009 (Purdue et al.) and 5,346,735 (Logan et al.), the disclosures of which are hereby incorporated herein by reference). Another type of peelable VSP is used, e.g., for high-profile meat cuts such as beef roasts, and consists of a pouch in which the meat product is contained. The interior of the pouch is evacuated so that it conforms to the contour of the packaged product. The pouch includes an outer, gas-impermeable portion that is peelably removable from an inner, gas-permeable portion to allow the meat product to re-bloom prior to placing the package in a retail display case. Such a package is exemplified in, e.g., U.S. Ser. No. 08/940,673, now abandoned entitled PACKAGE COMPRISING AN INNER, GAS-PERMEABLE ENCLOSURE AND AN OUTER, GAS-IMPERMEABLE ENCLOSURE PEELABLY ADHERED TO THE INNER ENCLOSURE and filed Sep. 30, 1997, the disclosure of which is hereby incorporated herein by reference.
Similar to a peelable VSP, a peelable xe2x80x9cmodified-atmospherexe2x80x9d package (xe2x80x9cpeelable MAPxe2x80x9d) includes a lidding film that separates into gas-permeable and gas-impermeable portions and which encloses, e.g., a fresh red meat or poultry product that is disposed within a support member having a peripheral flange to which the lid is secured. Prior to securing the lid to the support member, air is generally evacuated from the interior of the support member and replaced by a gas which extends the shelf-life of the packaged product. The gas-impermeable portion of the lid is peelably removed prior to retail display so that the packaged product is displayed in a state of re-bloom. An example of such a package is disclosed in, e.g., U.S. Pat. No. 5,686,126, the disclosure of which is hereby incorporated herein by reference.
While peelable VSP and MAP case-ready packages have been and continue to be successful, there is always a need and desire for improvements. For instance, as with any package, peelable VSP and MAP packages must contain some sort of labeling thereon that provides certain information to the consumer such as, e.g., product information, pricing, identification of the company from which the packages originated, etc. In order to be clearly visible to the consumer, such labels are placed on the lidding film because the transparent film is always facing the consumer in the retail display case so that both the packaged product and label can be inspected without having to move or handle the package. For the same reasons that it is desirable to package fresh red meat and poultry products at central processing facilities, it would also be desirable for the packages to be labeled with individualized information at the central processing facilities. Currently, however, such labels must be prepared and affixed to the gas-permeable portion of the lid at the retail facility following the removal of the gas-impermeable portion of the lidding film. This is necessary because lidding films for peelable VSP and MAP packages do not generally facilitate centralized printing and/or labeling. In the first place, it is not practical to apply the label to the upper, gas-impermeable portion of the lid because this portion is peeled from the packages and discarded prior to placing the packages in the retail display case. Secondly, placement of the printed image or label within the lidding film such that it remains on the package after the gas-impermeable portion is removed has also proven difficult. For example, commercially successful lidding films delaminate such that only a gas-permeable portion of a coextruded, multilayer film remains on the package after delamination, and it would be impossible to interject a label between two layers of a coextruded film. Labels or printed indicia applied to the side walls or bottom surface of the support tray are not attractive to consumers who are accustomed to labeling on the upper surface of packages. Thus, while case-ready packages of the type discussed above have obviated the need for in-store butchering, retail workers are still required to create and apply a unique label for each package, and it is presently not possible for a pre-printed image to be centrally applied to the lidding film such that it will remain on the package after the gas-impermeable portion of the lid is removed and the package is placed in a retail display case.
Another aspect of case-ready packages in which improvement is sought concerns the gas-permeable portion of the lidding film. Particularly with modified-atmosphere packages, it is often necessary that the gas-permeable lid portion contain very small perforations (e.g., less than about 250 microns in diameter) in order to increase the rate at which the packaged meat product re-blooms after removal of the gas-impermeable lid portion. While perforations do not present a problem from the standpoint of proper meat or poultry packaging, purge (juices) from packaged meat or poultry could potentially leak from the package through the perforations in the event that the packages are inadvertently tipped sideways or inverted after the gas-impermeable lid portion has been peeled from the package, e.g., in the retail display case or in a consumer""s shopping cart or grocery bag. Thus, it would be desirable that the remaining, gas-permeable portion of the lidding film not have perforations that would permit such leakage.
Accordingly, a need exists for a case-ready package with a lidding film that can carry product information and other indicia that is applied at a central processing and packaging facility but which remains on the package lid after removal of the gas-impermeable portion so that the information is visible to the consumer. A need also exists for a case-ready package that has a rapid rate of re-bloom without the necessity for open perforations in the remaining gas-permeable lid portion after removal of the gas-impermeable portion.
Those needs are met by the present invention which provides a laminate, comprising:
a. a multilayer, substantially gas-impermeable film capable of delaminating into a gas-permeable portion and a gas-impermeable portion, the gas-permeable portion in adherence with the gas-impermeable portion at a predetermined intra-film cohesive strength; and
b. a gas-permeable film bonded to the gas-impermeable film at a bond-strength that is greater than the intra-film cohesive strength between the gas-permeable and gas-impermeable portions of the gas-impermeable film, whereby, the laminate delaminates within the gas-impermeable film when the laminate is subjected to a delaminating force such that the gas-permeable portion of the gas-impermeable film remains bonded to the gas-permeable film.
Another aspect of the invention pertains to a package, comprising:
a. a product support member having a cavity formed therein, a product being disposed within the cavity; and
b. a lid comprising the laminate as described above that encloses the product within the cavity and is bonded to the support member.
A further aspect of the invention is directed to a method of making a package, comprising:
a. providing a product support member having a cavity formed therein;
b. placing a product in the cavity;
c. providing a laminate as described above; and
d. bonding the laminate to the support member as a lid to thereby enclose the product within the cavity of the support member.
As used herein, the term xe2x80x9claminatexe2x80x9d refers to a multiple-film composite structure having two or more films bonded together by any suitable means, including adhesive bonding; reactive surface modification (e.g., corona treatment, flame treatment, or plasma treatment); heat treatment; pressure treatment; etc., including combinations thereof.
As used herein, the term xe2x80x9cfilmxe2x80x9d refers to a thermoplastic material, generally in sheet or web form, having one or more layers formed from polymeric or other materials. A film can be a monolayer film (having only one layer) or a multilayer film (having two or more layers).
As used herein, the term xe2x80x9clayerxe2x80x9d refers to a discrete film component which is coextensive with the film and has a substantially uniform composition. In a monolayer film, the xe2x80x9cfilmxe2x80x9d and xe2x80x9clayerxe2x80x9d would be one and the same.
Unless otherwise specified herein, the term xe2x80x9cmultilayerxe2x80x9d refers to a film comprising two or more layers which are bonded together by one or more of the following methods: coextrusion, extrusion coating, vapor deposition coating, solvent coating, emulsion coating, or suspension coating.
As used herein, the terms xe2x80x9cextrusion,xe2x80x9d xe2x80x9cextrude,xe2x80x9d and the like refer to the process of forming continuous shapes by forcing a molten polymeric material through a die, followed by cooling or chemical hardening. Immediately prior to extrusion through the die, the relatively high-viscosity polymeric material is fed into a rotating screw, which forces it through the die.
As used herein, the term xe2x80x9ccoextrusion,xe2x80x9d xe2x80x9ccoextrude,xe2x80x9d and the like refer to the process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling, i.e., quenching. Coextrusion can be employed in film blowing, free film extrusion, and extrusion coating processes.
As used herein, the phrases xe2x80x9creactive surface modification,xe2x80x9d xe2x80x9creactively modifying the surface of,xe2x80x9d xe2x80x9creactively-modified surfacexe2x80x9d and the like refer to chemically altering the surface of a film in order to incorporate reactive species onto such film surface, e.g., to provide the film surface with auto-adhesion functionality (i.e., rendering the surface capable of adhering to another surface without the need for an adhesive). Specific examples of reactive surface modification include corona treatment, plasma (ionized gas) treatment, and flame treatment, with corona treatment being preferred. The surface of a film which has been subjected to reactive surface modification is referred to as a xe2x80x9creactively-modified surfacexe2x80x9d or, in the case of corona treatment, a xe2x80x9ccorona-treated surface.xe2x80x9d
As used herein, the terms xe2x80x9cdelaminate,xe2x80x9d xe2x80x9cdelaminating,xe2x80x9d and the like refer generally to the internal separation of a multilayer film within a layer and/or at an inter-layer (i.e., layer/layer) interface within the coextruded film when such film, or laminate of which the coextruded film is a component, is subjected to a delaminating force of sufficient magnitude. A laminate in accordance with the present invention includes at least one multilayer film having an intra-film cohesive strength which is both lower than the inter-film bond-strengths between the component films of the laminate and also lower than the intra-film cohesive strengths of the other films in the laminate. In this manner, the multilayer film component of the laminate internally separates, i.e., delaminates, when the laminate is subjected to a delaminating force that exceeds the intra-film cohesive strength of the coextruded film. The internal separation preferably occurs at a pre-selected layer/layer interface, and/or within a pre-selected layer, such that the multilayer film delaminates into a gas-permeable portion and a gas-impermeable portion.
As used herein, the term xe2x80x9cportion,xe2x80x9d as modified by the terms xe2x80x9cgas-permeablexe2x80x9d or xe2x80x9cgas-impermeable,xe2x80x9d refers to a delaminated segment of a multilayer film that includes one or more component layers of the multilayer film. In accordance with the present invention, a multilayer, gas-impermeable film delaminates into at least two portions, one of which is gas-permeable while the other is gas-impermeable.
As used herein, the term xe2x80x9cintra-film cohesive strengthxe2x80x9d refers to the internal force with which a film remains intact, as measured in a direction that is generally perpendicular to the plane of the film. In a multilayer film, intra-film cohesive strength is provided both by inter-layer adhesion (the adhesive strength between the layers which binds them to one another) and by the intra-layer cohesion of each film layer (i.e., the cohesive strength of each of the film layers). Intra-film cohesive strength is measured by the minimum amount of force (the xe2x80x9cdelaminating forcexe2x80x9d) required to internally separate (delaminate) a film in accordance with ASTM F904-91. In a monolayer film, intra-film cohesive strength is provided only by the intra-layer cohesion of the layer which constitutes the film.
As used herein, the term xe2x80x9cbond-strengthxe2x80x9d refers to the adhesive force with which two films in a laminate are joined to one another and is measured by the minimum amount of force required to ply-separate the two films in accordance with ASTM F904-91.
As used herein, the term xe2x80x9cgas-permeablexe2x80x9d refers to a film or film portion which admits at least about 1,000 cc of gas, such as oxygen, per square meter of film per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity). More preferably, a gas-permeable film or film portion admits at least 5,000, even more preferably at least 10,000, such as at least 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, and 50,000, and most preferably at least 100,000 cc of oxygen per square meter per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity). In accordance with the present invention, a gas-permeable film or film portion can itself have the aforedescribed levels of gas permeability or, alternatively, can be a film or film portion which does not inherently possess the aforedescribed levels of gas permeability but which is altered, e.g., perforated, to render the film gas-permeable as defined above.
As used herein, the term xe2x80x9csubstantially gas-impermeablexe2x80x9d refers to a film or film portion which admits less than 1000 cc of gas, such as oxygen, per square meter of film per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity). More preferably, a substantially gas-impermeable film or film portion admits less than about 500, such as less than 300, and less than 100 cc of gas, more preferably still less than about 50 cc, and most preferably less than 25 cc, such as less than 20, less than 15, less than 10, less than 5, and less than 1 cc of gas per square meter per 24 hour period at 1 atmosphere and at a temperature of 73xc2x0 F. (at 0% relative humidity).
As used herein, the phrase xe2x80x9cproduct support memberxe2x80x9d refers to a component of a package on or in which a product is disposed. Meat products are typically disposed in a tray-like package component comprising polymeric sheet material which has been thermoformed into a desired shape for supporting the meat product. A product support member preferably includes a cavity into which the product is disposed and a peripheral flange which provides a sealing surface for attachment of a lid to the support member to thereby enclose the product within the cavity.
As used herein, the phrase xe2x80x9cethylene/alpha-olefin copolymerxe2x80x9d generally designates copolymers of ethylene with one or more comonomers selected from C3 to C20 alpha-olefins, such as 1-butene, 1-pentene, 1-hexene, 1-octene, methyl pentene and the like, in which the polymer molecules comprise long chains with relatively few side chain branches. These polymers are obtained by low pressure polymerization processes and the side branching which is present will be short compared to non-linear polyethylenes (e.g., LDPE, a low density polyethylene homopolymer). Ethylene/alpha-olefin copolymers generally have a density in the range of from about 0.86 g/cc to about 0.94 g/cc. The term linear low density polyethylene (LLDPE) is generally understood to include that group of ethylene/alpha-olefin copolymers which fall into the density range of about 0.915 to about 0.94 g/cc. Sometimes linear polyethylene in the density range from about 0.926 to about 0.94 is referred to as linear medium density polyethylene (LMDPE). Lower density ethylene/alpha-olefin copolymers may be referred to as very low density polyethylene (VLDPE, typically used to refer to the ethylene/butene copolymers available from Union Carbide with a density ranging from about 0.88 to about 0.91 g/cc) and ultra-low density polyethylene (ULDPE, typically used to refer to the ethylene/octene copolymers supplied by Dow).
The phrase xe2x80x9cethylene/alpha-olefin copolymerxe2x80x9d also includes homogeneous polymers such as metallocene-catalyzed EXACT(trademark) linear homogeneous ethylene/alpha-olefin copolymer resins obtainable from the Exxon Chemical Company, of Baytown, Tex.; TAFMER(trademark) linear homogeneous ethylene/alpha-olefin copolymer resins obtainable from the Mitsui Petrochemical Corporation; and long-chain branched, metallocene-catalyzed homogeneous ethylene/alpha-olefin copolymers available from The Dow Chemical Company, known as AFFINITY(trademark) resins. The phrase xe2x80x9chomogeneous polymerxe2x80x9d refers to polymerization reaction products of relatively narrow molecular weight distribution and relatively narrow composition distribution. Homogeneous polymers are structurally different from heterogeneous polymers (e.g., ULDPE, VLDPE, LLDPE, and LMDPE) in that homogeneous polymers exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of length of all chains, i.e., a narrower molecular weight distribution. Furthermore, homogeneous polymers are typically prepared using metallocene, or other single-site type catalysts, rather than using Ziegler-Natta catalysts. Such single-site catalysts typically have only one type of catalytic site, which is believed to be the basis for the homgeniety of the polymers resulting from the polymerization.
As used herein, the term xe2x80x9colefinxe2x80x9d generally refers to any one of a class of monounsaturated, aliphatic hydrocarbons of the general formula CnH2n, such as ethylene, propylene, and butene. The term may also include aliphatics containing more than one double bond in the molecule such as a diolefin or diene, e.g., butadiene.
As used herein, the term xe2x80x9cpolyolefinxe2x80x9d refers to olefin polymers and copolymers, especially ethylene and propylene polymers and copolymers, and to polymeric materials having at least one olefinic comonomer, such as ethylene vinyl acetate copolymer and ionomer. Polyolefins can be linear, branched, cyclic, aliphatic, aromatic, substituted, or unsubstituted. Included in the term polyolefin are homopolymers of olefin, copolymers of olefin, copolymers of an olefin and a non-olefinic comonomer copolymerizable with the olefin, such as vinyl monomers, modified polymers of the foregoing, and the like. Modified polyolefins include modified polymers prepared by copolymerizing the homopolymer of the olefin or copolymer thereof with an unsaturated carboxylic acid, e.g., maleic acid, fumaric acid or the like, or a derivative thereof such as the anhydride, ester metal salt or the like. It could also be obtained by incorporating into the olefin homopolymer or copolymer, an unsaturated carboxylic acid, e.g., maleic acid, fumaric acid or the like, or a derivative thereof such as the anhydride, ester metal salt or the like.